Disk drive components in a magnetic direct access storage device (DASD), principally read/write heads and disk surfaces, are prone to corrosion by gaseous industrial by-products such as sulfur dioxide, hydrogen chloride, hydrogen sulfide, nitrogen oxides, and ammonia. When such pollutants combine with water vapor and dissolve, they form an acid electrolyte. The acid electrolytes may then corrode the metal used in disk drive components by forming corrosive products such as oxides and chlorides which have a larger crystallographic cell structure than the metal itself. The bulges formed of such corrosive products may then crash into the read/write head of the disk drive which is positioned to float a very small distance from the disk surface at a high rate of speed. Such crashes may reduce disk performance and cause possible read/write failures.
One attempt to reduce the effect of corrosive gases on disk components is to coat the metal surfaces with a carbon layer. However, this method has disadvantages because it increases the magnetic spacing between the read/write heads and the disk surface, thereby reducing the strength of the signal sensed by the read/write heads.
Another measure taken to reduce exposure of sensitive disk components to corrosive gases involves sealing the disk drive mechanisms within a housing or enclosure. The enclosure is typically formed of two casing members compressed together with a gasket disposed between their mating surfaces. However, it is almost impossible to create a perfectly sealed disk drive enclosure. Even with the best available match between the mating surfaces and the gaskets, a certain amount of polluted ambient atmosphere may still diffuse or otherwise enter the enclosure through the gaskets, or through leaks between the mating surfaces and the gaskets. The amount of leakage increases as the pressure differential between the inside and outside of the enclosure increases.
To minimize such diffusion, disk drive enclosures are often equipped with a breather filter. The breather filter provides a particularly easy path for air to flow into the enclosure. But to do so, the air must pass through one or more filtering media. The filtering media extract potentially harmful external gases and/or particulate contaminants contained in the air entering the enclosure.
However, a trend has developed in the disk drive manufacturing community to miniaturize the chassis or housing of a disk drive to a size amenable for incorporation into miniature personal computers, such as lap-top or notebook computers, for example. Various industry standards have emerged that specify the external housing dimensions of small and very small form factor data storage systems. One such recognized family of industry standards is the PCMCIA (Personal Computer Memory Card Industry Association) family of standards, which specifies both the dimensions for the data storage system housing and the protocol for communicating control and data signals between the data storage system and a host computer system coupled thereto. Recently, four families or types of PCMCIA device specifications have emerged. For example, a Type-I PCMCIA data storage system must be fully contained within a housing having a maximum height dimension of 3.3 millimeters (mm). A Type-II PCMCIA device housing must not exceed a maximum height of 5.0 mm in accordance with the PCMCIA specification. A maximum height of 10.5 mm is specified for the housing of Type-III PCMCIA devices, and Type-IV devices are characterized as having a maximum housing height dimension in excess of 10.5 mm.
The size constraints specified by the PCMCIA and other industry standards make incorporation of existing filter technology into small and very small form factor drives increasingly difficult. In fact, some PCMCIA Type-III and Type-II devices contain no breather filter at all. For these drives, diffusion of materials into the drives will occur through leaks in the seal with subsequent reaction with the disk surfaces and read/write heads occurring at an uncontrolled rate.
Accordingly, there exists a need in the data storage system manufacturing industry for a very compact enclosure assembly for a disk drive that protects sensitive disk components encased therein from potentially harmful pollutants. The need is particularly strong for a reliable disk drive which is too small to incorporate existing filter technology. There is an additional need to reduce the magnetic spacing between the read/write heads and the disk surface.